Yes - RAK have been really interested in getting ports of Espruino for their devices, so there is some hope that there may be official support for that at some point :)

Really the only gotcha is adding support for LoRaWan on SX127x to Espruino. You could install Espruino on the RAK813 and send LoRa packets on the SX127x right now - it's just getting the relevant stuff to have it running on LoRaWan :)

yep, LoraWan is more complex then just Lora.
I have been playing with it since a couple of years.
Arduino.org was developing a similar module that I have for testing (pic attached).
Since " .org" is now defunct I guess we could start from their library, for porting. Otherwise there is lmic... but probably architecturally more complex.